Carbon nanotubes have been proposed to have utility in a number of applications due to their large effective surface area, mechanical strength, and thermal and electrical conductivity, among other properties. Many of these applications are particularly well suited for carbon nanotubes that have been grown on carbon fiber substrates. When grown on carbon fiber substrates, the properties of the carbon fiber substrates can be enhanced by the carbon nanotubes. For example, when carbon nanotubes are grown thereon, the mechanical strength of the carbon fiber substrates can be enhanced, and the carbon fiber substrates can become electrically conductive.
In order to synthesize carbon nanotubes, a catalyst is generally needed to mediate carbon nanotube growth. Most often, the catalyst is a metal nanoparticle, particularly a zero-valent transition metal nanoparticle. A number of processes for synthesizing carbon nanotubes are known in the art including, for example, micro-cavity, thermal- or plasma-enhanced chemical vapor deposition (CVD) techniques, laser ablation, arc discharge, flame synthesis, and high pressure carbon monoxide (HiPCO) techniques. Generally, such processes for synthesizing carbon nanotubes can involve generating reactive gas phase carbon species under conditions suitable for carbon nanotube growth.
Synthesis of carbon nanotubes on solid substrates can be carried out using many of these techniques. However, it is considered very difficult in the art to grow carbon nanotubes on carbon fiber substrates. It is believed that a primary impediment to this effort has been the difficulty of dissolving sufficiently high quantities of the reactive gas phase carbon species in metal nanoparticle catalysts to support carbon nanotube growth. Unlike other types of substrates (e.g., metals, glass and the like), carbon fiber substrates and the reactive gas phase carbon species are both composed of carbon, which greatly increases their interaction with one another and makes the reactive carbon species less likely to dissolve in the metal nanoparticles to facilitate carbon nanotube growth. In addition, unfavorable interactions between metal nanoparticles and carbon fiber substrates can further limit the ability of reactive gas phase carbon species to diffuse into the metal nanoparticles, further impeding carbon nanotube growth.
In view of the foregoing, reliable processes for growing carbon nanotubes on carbon fiber substrates would be of substantial benefit in the art. The present disclosure satisfies this need and provides related advantages as well.